Currently, many furniture are designed to be adjustable in elevations, such as desks, chairs, etc. so as to have a preferred arrangement to make user feel comfortable in use.
However after adjusting, the parts of the furniture must be fixed. In one prior art computer desk, a table plate is fixed by an air pressure bar and a supporting rod. A telescopic tube is embedded into the support rod. The telescopic tube resists against a frame plate. One side of the telescopic tube has a plurality of positioning holes for screwing. The movement of the air pressure bar can adjust the elevation of the table plate. Then a retainer is used to fix the table plate to a supporting rod continuously so that the elevation of the table plate is adjusted. When a proper height is achieved, screws pass through the positioning holes of the telescopic tube so as to position the frame plate.
However in above prior art, the adjustment of the table plate is continuous, while the positioning is difficult, and particularly to when the computer desk has supported with a computer and other devices. The supporting of the air pressure bar and supporting rod can not prevent the screw from loosing (especially when it is used for a long time and thus the material is fatigue).